It was shown in previous publications that these 2 allergens share common IgE-epitopes resulting in immunological cross-reactivity within the sensitized patient population 3, 5.
In addition to the immunochemical works on these allergens, a lot of antigenic analyses were done to identify and map the potential IgE- and T cell epitopes of these 2 allergens. Pectate lyases are pectin-degrading enzymes expressed in large amounts during pollen germination to degrade the pollen wall and emergence of the pollen tube 4. One such allergen is the pectate lyase reported from ragweed (designated as Amb a 1) as well as from mugwort (Art v 6) 3. Many of these allergens are used worldwide for diagnostic and therapeutic purposes. Several allergens have been isolated and characterized from these plants. A number of plants belonging to the families of Asteraceae or Compositae such as ragweed ( Ambrosia artemisiifolia), mugwort ( Artemisia vulgaris), and feverfew ( Parthenium hysterophorus) are important sources of inhalant allergens in many parts of Europe and America 1, 2. Certain economically important plants, which are not strictly wind-pollinated, may also trigger IgE-mediated occupational allergy in working individuals.
Grass pollens, weeds, and road-side ornamental trees are the primary sources of allergens. The global prevalence of IgE-antibody mediated respiratory allergy caused by airborne pollen grains is increasing at an alarming rate. In conclusion, Hel a 6 serves as a candidate molecule for diagnosis and immunotherapy for weed allergy. Two antigenic regions were found to be commonly shared by these 3 allergens, which could be crucial for cross-reactivity. Several putative B cell epitopes were predicted and mapped on these 3 allergens. The cross-reactivity was further substantiated by the mediator release when Hel a 6-sensitized effector cells were cross-stimulated with Art v 6 and Amb a 1. The IgE-cross reactivity was observed between Hel a 6 and its ragweed and mugwort homologs. Hel a 6 displayed a high degree of sequence conservation with the pectate lyase allergens from related taxonomic families such as Amb a 1 (67%) and Art v 6 (57%). Hel a 6 was folded, and its melting curve showed reversible denaturation in which it refolded back to its native conformation from a denatured state. The effect of various physicochemical parameters such as temperature, pH, and calcium ion on the functional activity of Hel a 6 revealed a stable nature of the protein. Monomeric Hel a 6 displayed pectate lyase activity. Hel a 6 exhibited allergenic activity by stimulating mediator release from basophils. The patients were of Indian origin and suffering from pollinosis and allergic rhinitis. Hel a 6 reacted with IgE-antibodies from 57% of 39 sunflower-sensitized patient sera suggesting it to be a major allergen. Natural Hel a 6 was purified from sunflower pollen by anion exchange and gel filtration chromatography.
The present study describes the comprehensive characterization of a major sunflower allergen Hel a 6. Sunflower pollen was reported to contain respiratory allergens responsible for occupational allergy and pollinosis.
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